Synthesis, crystal structures and DFT studies of Co(ii) and Zn(ii) coordination polymers of terephthalate and 4,4′-trimethylenedipyridyl ligands for removal of dibenzothiophene from a model fuel oil

Abstract

The negative environmental and human health challenges posed by sulfur oxides that are released upon combustion of fuel oils containing sulfur necessitate the development of methods for its removal, and hydroprocessing is the conventional technique. However, dibenzothiophene and its substituted derivatives are refractory. As such, the coordination polymers (CPs): [Co(tmdp)₄Cl₂]_n1 and [Zn(tpa)₂(tmdp)₂·(H₂O)₂]_n2, where tmdp is trimethylenedipyridine and tpa is terephthalic acid, were synthesized for application in adsorptive separation to selectively remove the refractory compounds. Spectroscopy techniques (UV-vis and FT-IR), single crystal XRD, micro-elemental analysis, TGA and SEM were used for characterization. Heat activation of both CPs was carried out to remove lattice solvent molecules before applying them in adsorption. Both CPs, showed good adsorption of dibenzothiophene (DBT) with maximum adsorption capacities of 49 mg g⁻¹ and 44 mg g⁻¹, respectively. The adsorption studies and theoretical studies carried out pointed to physisorption as the mechanism for adsorption of DBT in both CPs with interactions being predominantly dispersion forces between the ligands and DBT.